Preparation of vinylidene cyanide by pyrolysis of novel 4, 4-disubstituted cyclohexenes



Patented Apr. 4, 1950 PREPARATION OF VINYLIDEN E CYANIDE BY PYROLYSIS OFNOVEL 4,4-DISUBSTI- TUTED CYCLOHEXENES Alan E. Ardis, Cuyahoga Falls,Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., acorporation of New York No Drawing. Original application February 7,

1948, Serial No. 6,999. Divided and this application December 3, 1948,Serial No. 63,434

10 Claims. (Cl. 260-4653) This invention relates to a method for thepreparation of vinylidene cyanide which method involves the pyrolysis ofcertain 4,4-disubstituted cyclohexenes.

I have discovered that vinylidene cyanide, also called 1,1-dicyanoethylene, a liquid compound of the formula when present in monomericform, may be readily prepared in excellent yields by the pyrolysis ofdisubstituted cyclohexenes of the formula wherein each of X and Y isselected from the class consisting of -CN and -CONH2 radicals, X and Ybeing the same or different.

The 4,4-disubstituted cyclohexenes which are pyrolyzed to obtainvinylidene cyanide in accordance with this invention have not heretoforebeen prepared but may be obtained in a variety of ways. One method ofarriving at compounds in which X and Y are the same consists in reacting4,4-dicarboxy cyclohexene, a known compound,

with thionyl chloride or other substance which will replace the hydroxylhydrogen atoms with chlorine, and then reacting the 4,4-cyclohexenedicarbonyl chloride thus formed with ammonia. The new compound wherein Xand Y are both -(fi-NH2 i. e., 4,4-dicarbamyl cyclohexene, is therebyobtained. From this diamide the dinitrile 4,4-dicyano cyclohexene, thenew compound wherein both of X and Y are -CN, is obtained simply bydehydration in the usual manner.

The new compound wherein X and Y are diff erent, that is,4-cyano-4-carbamyl cyclohexene, may be prepared, for example, byreacting butadiene-1,3 with an alkyl ester of alpha cyano acrylic acid(the preparation of which is disclosed in my copending applications,Serial No. 731,863. filed March 1, 1947, now Patent No. 2,467,926, andSerial No. 751,471 filed May 29, 1947, now Patent No. 2,467,927) to forma 4-cyano-4-carboalkoxy cyclohexene, also a new compound, and thenconverting the carboalkoxy group to the carbamyl group by reaction withammonia. 4,4-dicyano 2 cyclohexene is also obtainable by dehydrating the4-cyano-4-carbamyl cyclohexene.

The reactions described above may be formulated as follows:

G 0 OH 0001 0 ONE,

S0011 2NH: 00011 COC1- CONE;

OONH: ON

2O 0 ONH: ON

Dehydrating Agent CN CN coon o 0 N or:

NH: -Hz0 c o 0 R i o oNrn ON Dehydrating Agent As disclosed hereinabove,vinylidene cyanide is obtained by the pyrolysis of any of the compoundsof the general formula wherein X and Y have the meaning set forthhereinabove. Monomeric vinylidene cyanide is easiest obtained in highestyields when the compound pyrolyzed is 4,4-dicyano cyclohexene, althoughvinylidene cyanide may also be readily obtained in good yield by thepyrolysis of the other compounds of this formula.

The products of the pyrolysis reaction are vinylidene cyanide andbutadiene-l,3. In addition to vinylidene cyanide and butadiene, water isalso obtained when the starting compound is a disubstituted cyclohexenecontaining one or more carbamyl (-CONH2) groups.

The pyrolysis reaction can be conducted in several different manners.For example, one method involves passing vapors of the'4A-disubstitutedcyclohexene through a heated metal tube, preferably brass, which isconnected to a receiver, preferably provided with external cooling meansso as to liquefy the pyrolysis product. Variations in this methodinvolve the use of a glass pyrolysis tube instead of a metal tube, orpyrolyzing the starting material over a hot resistance wire. Thepyrolysis reaction is preferably conducted at reduced pressures, andespecially from 2 to 50 mm., although pressures up to and includingatmospheric pressure are operative.

The temperature at which the pyrolysis is conducted may be variedwidely. Temperatures in the range of 400 C. to 800 C. are operative withthe preferred range being from 550 C. to 700 C.

The product of the pyrolysis, usually collected as a liquid, is amixture of vinylidene cyanide, unreacted 4,4-disubstituted cyclohexeneand butadiene, water also being present when the starting materialcontains one or more CONH2 groups. The vinylidene cyanide can beseparated from the pyrolysis product by several methods. For example, apreferred method consists in evaporating oil the volatile butadiene andfractionally distilling the remainder of the pyrolysis reaction mixture,preferably at reduced pressures, whereupon a fraction consistingsubstantially of vinylidene cyanide is obtained.

A second useful method consists in extracting the vinylidene cyanidefrom the reaction mixture by the use of a, solvent, preferably one fromwhich the vinylidene cyanide will crystallize. This is done, forexample, by mixing th liquid product and a substance such as dry tolueneor similar aromatic hydrocarbon, preferably in equal volumes, andcooling the mixture to a temperature of approximately 40 C. whereuponmonomeric vinylidene cyanide separates from the liquid mixture in theform of crystals which are easily isolated, for example, by filtration.High yields of very pure vinylidene cyanide, in the monomeric form, areobtained by this method.

vinylidene cyanide polymerizes quite rapidly in the presence of water toform a'solid polymer. Consequently, when water is present in thepyrolysis reaction mixture, vinylidene cyanide may be isolated byallowing polymerization to proceed and then separating the solidpolymerized vinylidene cyanide from the other products by filtering orthe like. The polymer may then be depolymerized by heating, preferablyat 170 to 250 0., to obtain monomeric vinylidene cyanide.

When using other methods of separation, it is desirable that thevinylidene cyanide be stabilized against polymerization from the timethat it is formed. This may be accomplished by using a suitablevinylidene cyanide stabilizer (that is, a polymerization inhibitor)which may be mixed with the 4,4-disubstituted cyclohexene prior topyrolysis or placed in the receiver for the pyrolysis reaction product.Such a stabilizer is also preferably present in the receiver used tocollect the vinylidene cyanide when it is separated by distillation.Suitable vinylidene cyanide stabilizers include phosphorus pentoxide andphosphorus pentasulfide, which are preferred, as well as antimonypentoxide, concentrated sulfuric acid and other materials reactive withwater, since polymerization is catalyzed by even small amounts ofhydroxyl ion. The stabilizer may be present in any desired amount but ingeneral as little as 0.5 to 3.0% based on the amount of monomer issufficient to prevent polymerization for extended periods of time.

The following examples are intended to illustrate the preparation of4,4-disubstituted cyclohexenes and the pyrolysis oi. such compounds tovinylidene cyanide. It is not intended, however,

4 to limit the invention thereto, for there are, of course, numerousmodifications. All parts are by weight.

Example I 116 parts of 4,4-dicarboxy cyclohexene are refluxed for 63hours with 650 parts of thionyl chloride. The unreacted thionyl chlorideis removed by distilling at reduced pressure. The residue is thendiluted with three times its volume of anhydrous ether and this solutionadded dropwise with stirring and cooling to a dry ether solution ofammonia. Additional ammonia is bubbled through the reaction mixtureduring the addition of the ethereal solution in order that an excess ofammonia can b maintained throughout the reaction. The solid which formsis filtered, washed with water and recrystallized from methanol. It isidentified as 4,4-dicarbamyl cyclohexene (nitrogen analysis: theory16.7%, found 16.3%) and is secured in substantially quantitative yield.

Example II 120 parts of 4,4-dicarbamyl cyclohexene, obtained as inExample I, are mixed with 189 parts of phosphorus pentoxide as adehydrating agent, and the mixture fractionally distilled whereuponthere is obtained 60 parts of a fraction (B. P.

66 C./l mm.) which upon purification is identified as 4,4-dicyanocyclohexene (M. P. 36 C.: nitrogen analysis: theory 21.2%, found 20.1%).

Example HI n 1.40) is obtained in good yield.

Example IV When 4,4-dicarbamyl cyclohexene as prepared in Example I ispyrolyzed as in Example II over a nickelchromium wire at a temperatureof 600 C. in the presence of phosphorus pentoxide, vinylidene cyanide isagain obtained in substantial yield.

Example V hexene thus prepared is then treated with 1.2

moles of concentrated ammonium hydroxide. The solid thus formed isfiltered, washed with a small amount of cold ethanol and thenrecrystallized from methanol. It is identified as 4-carbamyl-4-cyanocyclohexene (nitrogen analysis; theory 18.7%. found 18.8%).

Example VI 15 parts of 4-carbamyl-4-cyano cyclohexene prepared as inExample V are mixed with 20 parts of phosphorus pentoxide and suiilcienttricresyl phosphate to give an intimate mixture. This mixture is thendistilled giving a 64% yield of 4,4-dicyano cyclohexene (B. P. 66/1 mm.,110/11 mm).

Example VII 26.5 parts of 4,4-dicyano cyclohexene are heated and thevapors passed at a temperature of 670 C. and a pressure of 9 mm. througha brass pyrolysis tube containing brass chain packing. The pyrolysisreaction product is then distilled at a pressure of 10 mm. whereupon 5.2parts (56%) of monomeric vinylidene cyanide are obtained.

Example VIII The pyrolysis of Example VII is repeated in the presence of1 part of phosphorus pentoxide. Upon distillation of the reactionproduct at a pressure of 10 mm. a 58% yield of monomeric vinylidenecyanide (M. P. 8 C.; n=1.4440) is obtained.

When 4-cyano-4-carbamyl-cyclohexene prepared as in Example V ispyrolyzed under the conditions set forth hereinabove and the reactionproduct distilled, vinylidene cyanide is also obtained as the principalproduct.

vinylidene cyanide prepared by the method of this invention is veryvaluable for the preparation of polymers and copolymers suitable assynthetic rubbers, synthetic resins, and plastics. Furthermore,polymeric vinylidene cyanide and copolymers of vinylidene cyanide andother ma-- terials polymerizable therewith, may be spun into syntheticfilaments which possess may valuable properties including great tensilestrength, flexibility, and resistance to chemicals. Monomeric vinylidenecyanide, as well as the compounds from which it isobtained as disclosedherein, may also be used for insecticidal and fungicidal purposes aswell as for many other uses.

Although specific examples are included herein, it is not intended tolimit the invention thereto, for numerous modifications will be apparentto those skilled in the art, and are within the,v

scope of the appended claims.

This application is a division oi! copending application, Preparation ofvinylidene cyanide by pyrolysis oi novel 4,4-disubstituted cyclohexenes,Serial No. 6,999, filed February '7, 1948.

I claim:

1. The method which comprises pyrolyzing a compound of the formulawherein each of x and Y is a member of the class consisting of -CN andCONH: radicals at a temperature 01 400 C. to 800 C. and separatingvinylidene cyanide from the pyrolysis reaction mixture.

2. The method which comprises pyrolyzin: a compound of the formulawhereinx andYareamemberottheclass consistinotCNand-CONH:radicals,at-a

sure of from 2 to mm. and separating vinylidene cyanide from thepyrolysis reaction mixture.

3. The method which comprises pyrolyzing 4,4-dicyano cyclohexene at atemperature of 400 C. to 800 C. and recovering vinylidene cyanide fromthe pyrolysis reaction mixture.

4. The method which comprises pyrolyzing 4,4-dicyano cyclohexene at atemperature of 450 C. to 800 C. and a pressure of 2 to 50 mm. andrecovering vinylidene cyanide from the pyrolysis reaction mixture.

5. The method which comprises pyrolyzing 4,4-dicyano cyclohexene at atemperature of 600 C. to 700 C. and at a pressure of 2 to 50 mm. andseparating vinylidene cyanide from the pyrolysis reaction mixture.

6. The method which comprises pyrolyzing a compound of the formulawherein X and Y are selected from the class consisting of CN and --CONH2radicals, at a temperature of 400 C. to 800 C., collecting the pyrolysisreaction mixture in the presence of phosphorus pentoxide and separatingmonomeric vinylidene cyanide from the pyrolysis reaction mixture.

'l. The method which comprises pyrolyzing a compound of the formulawhereinX and Y are selected from the class cousisting of -CN and CONH2radicals, at a temperature (if-450 C. to 800 C. and at a pressure oifrom 2 to 100 mm, collecting the pyrolysis reaction mixture in thepresence or phosphorus pentoxide', and separating monomeric vinylidenecyanide from the pyrolysis reaction mixture.

8. The method which comprises pyrolyzing 4,4-clicyano cyclohexene at atemperature of 450 C. to 800 C., collecting the pyrolysis reactionmixture in the presence of phosphorus pentoxide, and separatingmonomeric vinylidene cyanide from the pyrolysis reaction mixture.

9. The method which comprises pyrolyzing 4,4-dicyano cyclohexene at atemperature of 600 C. to 700 C. and a pressure of 2 to 50 mm.,collecting the pyrolysis reaction mixture in the presence of phosphoruspentoxide, andseparating monomeric vinylidene cyanide from the pyrolysisreaction mixture.

10. The method which comprises pyrolyzing 4,4-dicyano cyclohexene at atemperature 0! 600 C. to 700 C. and a pressure of-2 'to 50 mm.,collecting the pyrolysis reaction mixture in the presence of phosphoruspentoxide, and distilling the reaction mixture to obtain monomericvinylidene cyanide.

ALAN E. ARDIS.

UNITED STATES PATENTS Number Name Date temperature 01' 400' C. to MC(Itid 0t 0 W r 3,454,849 BOhWQl'dlQ NOW, 19

Certificate of Correction Patent N 0. 2,502,412 April 4, 1950 ALAN E.ARDIS It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows: I

Column 4, line 45, for 1.40 read 1.440; column 5, line 34, for the wordmay read many;

and that the said Letters Patent should beread with these correctionstherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 15th day of August, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

1. THE METHOD WHICH COMPRISES PYROLYZING A COMPOUND OF THE FORMULA